The present invention relates to medical devices and methods of using same, and more particularly such devices and methods for producing bradycardia in the human body.
Dive reflex, also known as diving reflex, is the mechanism through which the human body defends itself from hypothermia and resulting death, when submerged in cold water. The reflex is most graphically illustrated by the resuscitation of children, who have been submersed in farm ponds during the winter for periods exceeding the threeminute brain-death criterion. In dive reflex, the body, through selective vasoconstriction, isolates those tissues with extended anaerobic capability from those with relatively little anaerobic capability (the heart and brain). Consequently, circulation to the extremeties is greatly diminished, while circulation to the brain and heart continues at generally adequate levels. Additionally, the pulse-rate slows and a relatively constant blood pressure is maintained. Typically, the resulting minimum dive-reflex pulse-rate is approximately 60 to 70 percent of the quiescent rate. By trunking blood to the brain and heart, and slowing the pulse-rate, the body is able to supply the required oxygen to both the brain and the heart for extended periods of cold water submersion.
Although the dive reflex phenomenon has been known for a considerable period of time, the triggering mechanism has only recently been determined. Through selective anatomica immersion, it has been determined that the receptor mechanism is located in the face. See J. Finley et al, Autonomic Pathways Responsible for Bradycardia on Facial Immersion, Journal of Applied Physiology, Volume 47(6), Pages 1218-22 (December 1979). More recently, it has been hypothesized that the triggering receptor is the facial nerve which surfaces at the cheeks, forward of the ears to the nose. The facial nerve communicates with the auricular branch of the vagus nerve, which provides the autonomic pathway to the heart through the general visceral efferent fibers (parasympathetic branch of the vagus nerve). The application of a cold stimulus to the facial nerve induces dive reflex and slows the pulse-rate through its communication with the vagus nerve.